Oilfield Consultant in Surface and Subsea Wellheads Equipment,Christmas Trees,Flow Control Equipment,Seals(Elastomerics & Metal-to-Metal)          

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                                         1.3.  TUBING  BONNETS
 This element is a transition adapter flange between the tubing head upper flange and the Christmas tree (so called Flow Tree), and at the same time make seal inside with the nose of the tubing hanger or a sub adapter that assures no leakage,in the production bore.

There are many styles available in the market, and the use of a particular one has an explanation with the type, of well, conditions.

We can generally divide in two major groups:



TUBING BONNETS SUSPENSION SYSTEMS: Are those who can suspend the tube string, acting like a tubing hanger, due to the STUB ACME ( generally used), internal thread, and a so called PLUG BUSHING (in the right   image is the part in blue), which is the suspensor element of the tubing string, also it has to make a seal in between of both


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The figure at left shows a standard shape for a tubing bonnet suspension type. Typically is arranged for plug bushing suspension systems and may carry inside one of the plug bushings shown below making of course the pertinent arrangements, for each model

Notice the test port fitting  in the right side  of the bottom flange, it allows the  testing the seals and the ring gasket area in the major flange.

PLUG BUSHING,  there is two versions: one of the left is a non thread version, that uses a threaded nut(Gland Nut) to be attached to the tubing bonnet, and the one of the right has the thread in the bottom of the coupling.Why one or the other? it depends of the final orientation of the Christmas Tree.

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This element is used where typically reciprocant wells conditions demand the use of a rough element enough for heavy loads for pulling up and down the tubing string, during the activation of the well.

Both designs has seals O-Rings elements, and a threaded connection to the tubing string, as well as the lifting threads , in the middle both has the back-pressure thread connection as well, that allows a threaded plug H-BPV to be passed by the Christmas tree above, in the operation for well's work over, this is a safety feature.

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This tubing bonnet is another style suspension system that allows by a simple threaded connection box inside the bottom flange to connect and suspend all the tube string downhole, this design is widely used in many oil field and generally for pumping used, notice the convenient 1/2" LP test port.




       The threads for this tubing bonnet may vary and are as different as the tubing string attached, most popular used are this mix:

          SERIES EUE 8RD

             SERIES  API LP
2-3/8" OD EUE 8RD BOX x PIN   2-3/8" API LP BOX x PIN
2-7/8" OD EUE 8RD BOX x PIN   2-7/8" API LP BOX x PIN
3-1/2" OD EUE 8RD BOX x PIN   3-1/2" API LP BOX x PIN

                                  The working pressures for this particular tubing bonnet may vary from 2M up to 5M PSI WP.

TUBING BONNETS SEALING SYSTEMS: Are those tubing bonnets different than the preceding described, where the element only is responsible for the seal of the nose's hanger, and the suspension of the tubing string is accomplished by the tubing hanger, that is landed in the tubing head's bowl, so in that way there is no suspended load attached to the tubing bonnet.

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This images shows tubing bonnets single completion styles 11-5M PSI x 3-1/8-5M PSI where the element only makes nose seal by two O-Rings installed in the tubing hanger color magenta.

This kind of oil completions are widely used in working pressures ranges from 2M PSI up to 15M PSI making of course appropriate sealing system adequate for the pressure to work, for instance in 15M PSI you'll not see any O-Ring in the tubing hanger, and instead of that there is a nose with a metal-to-metal preparation to make seal to the tubing bonnet by pure and simple metal inference.




When the well's completion is dual so that mean double tubing string, the tubing bonnets are transformed in Dual Tubing Bonnets allowing the use of dual tubing hangers for that purpose, and also allowing the nose of the dual tubing hanger to make seal as well.

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This image shows one of the many configurations of dual tubing bonnets it allows the installation of a set(pair) dual valve D-5  in the top of the studded preparation; this a generic drawing. There are other arrangements to connect the studded preparation to a Block Master Valve, in such case the top must be the same dimensions and studs preparation that the bottom Block Master Valve's Flange. It is also useful the Hold -Down Flange configuration in this designs of Dual Tubing bonnets, because the orientation of the Christmas Tree will be more easy.

Notice that in many cases this dual tubing bonnets may be integral with the block master valve design.In all the cases it has to have a test port, and in other applications a control line port preparation.




Updated on:01/20/04Copyright @2003 Daniele Molaro Consulting

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